In order to fix an artificial tooth, first, the upper surface of the gingival mucosa is incised; second, a hole is drilled into the jaw bone; third, an artificial dental root is implanted into the hole; fourth, a shock-absorbing material and a crown of the tooth is constructed 2-3 months later, namely, after the artificial dental root has been fixed by newly grown bone.
In such an artificial dental root, generally speaking, threads are cut on one end of a round rod-shaped material so as to prevent the root from coming off, and the other end is used as a crown attaching portion. A hole, whose diameter is almost the same as that of this threaded portion, is drilled in the jaw bone, into which the threaded portion is implanted. The conventional artificial dental root used to be fixed by allowing the new bone to grow between the threads.
Such an artificial dental root, however, requires the drilling in the jaw bone of a hole whose diameter is almost the same as that of the crown-attaching portion. If the diameter of this hole is large, it becomes difficult to drill the hole in the jaw bone in order to implant the artificial dental root into a narrow jaw bone, which leads to frequent injuries to the jaw bone. On the other hand, however, there is a drawback in that if the diameter of the hole, that is, the diameter of the artificial dental root, is made small, the strength required for the root is not obtained, and it is likely to break or become damaged, or at the same time, sink further into the jaw bone owing to a force exerted onto the artificial dental root.
The Japanese Patent Publications Kohkoku Showa 53-2279 and Kohkoku Showa 53-877 and U.S. Pat. No. 4,086,701 (corresponding to the aforementioned two publications) have been known as one which is designed to stabilize and strengthen the artificial dental root with respect to biting impacts.
The aforementioned Japanese Patent Publications 53-2279 provided a horizontal flange member (disk-like flange member) for the artificial dental root which acted as a main stabilizing seat against external force. Although this artificial dental root mainly supported external stress by means of the horizontally extending diske-like flange member, the stress was concentrated onto the thin portion of the disk-like flange member, the portion of which sometimes proved to be insufficient in terms of strength. In particular, though strong against stress applied in a vertical direction, the disk-like flange member was weak against stress exerted in an oblique direction. This indicated that it was practically difficult to provide sufficient strength to relieve the concentration of biting stresses.
Similarly, an artificial dental root equipped with a stopper portion has been disclosed in Japanese Patent Publication Kohkai Showa 60-135042; however, this was not designed to support biting stresses and could not provide sufficient strength and relieve concentrated biting stresses.
In addition, the aforementioned Japanese Patent Publication Kohkoku Showa 53-877 describes an artificial dental root provided with an anchor ring (a washer-like flange member) which is inserted into a cavity in the jaw bone and acts as a stabilizing seat.
Since this washer-like flange member, however, was made of porous ceramics and screwed to the root body, it did not have sufficient strength and stress-relieving action against external stresses even though it was effective in stabilizing the artificial dental root.
In particular, stress was concentrated onto the screw-joint portion, the washer-like flange member was very likely to chip off. It also had a drawback that if a joint portion such as a screw is provided in the implanted part of the bone, this may easily produce a pocket of a nest of baccili.
These drawbacks are particularly noticeable in the case where, in general, mechanically weak calcium phosphate ceramics or bioactive ceramic materials are used in the artificial dental root.